The present invention relates to a molded lens used in an optical pickup device and to a molding die for the molded lens.
An optical pickup device used for recording and reproducing of information employing an optical information recording medium (an optical disc) is constructed by combining various types of optical elements such as an objective lens, a collimator, a coupling lens and others.
These optical elements are formed by injecting melted resins in a cavity of a molding die for molding a lens, in many cases. Hereafter, in the present specification, an optical element manufactured through injection molding employing a molding die is expressed as “a molded lens”.
With miniaturization of an optical pickup device in recent years, there are disclosed various technologies about miniaturization of a molded lens that constitutes an optical pickup device (see TOKKAI No. 2002-243915 for example).
A molded lens described in TOKKAI No.2002-243915 is a lens having an outer form that is in a circular shape whose center is on an optical axis wherein outer circumference portions on the top and the bottom of the lens are cut off, and either one optical surface of both optical surfaces including the surface of incidence (first surface) and the surface of emergence (second surface) is cut off and the other optical surface is not cut off, namely, an outer circumference of the other optical surface is kept to be in a circular form. By cutting off the outer circumference portions on the top and the bottom of the lens, a length (height) of the molded lens in the direction perpendicular to the optical axis of the molded lens can be shortened, and miniaturization of the lens itself can be attained.
However, further miniaturization of the optical pickup device is demanded in recent years, and there is caused a problem that a molded lens which is smaller than the molded lens in TOKKAI No.2002-243915 is demanded.
As shown in FIG. 4(a), on ordinary molded lens 100 having an outer shape in a circular form, there is provided bracket 102 for holding the lens at the position to cover the outer circumference of optical functional surface 101. The symbol 200 is a box-shaped cartridge for housing therein a plurality of lenses 100, and on a part of left and right wall members 201, there is provided a vacant space 202 that extends in the longitudinal direction (the direction perpendicular to the page). Then, by holding brackets 102 on both left and right sides in the vacant space 202, a plurality of lenses 100 are housed in the longitudinal direction the cartridge 200, in the structure.
On the molding die used for injection molding, there is usually provided a hole through which air in the cavity is driven out when melted resins are injected in the cavity. Therefore, when melted resins entered a part of this hole are solidified when molding a lens, “a flash” which is projected slightly from the surface is generally formed on the molded lens.
Though this flash is sometimes projected in the radial direction from the outer circumference of the lens, it is hardly caused that flashes on adjoining two molded lenses 100 touch each other to be damaged, because each lens 100 is rotatable freely on a horizontal plane crossing the optical axis at right angles under the condition that the lens is held in the vacant space 202, even when ordinary molded lenses 100 each having a circular outer form are housed continuously in cartridge 200.
However, in the case of molded lens 300 whose outer circumference portion is cut out (see FIGS. 4(b) and 4(c)) such as one described in TOKKAI No. 2002-243915, a plurality of lenses 300 are held by causing the cut out portion to touch a part of left and right wall members 201 of the box-shaped cartridge.
In this case, when flash 301 (see FIG. 4(b)) is projected from an outer circumference (a portion other than a cut out portion) of lens 300, in the radial direction, there has been a fear that flashes 301 on the two adjoining molded lenses touch each other to be damaged, and a part of the damaged flash 301 is stuck on the optical surface of lens 300, because a movement of each lens 300 is regulated in a horizontal plane that crosses the optical axis at right angles by left and right wall members 201.
Further, there is an occasion where flash 301 is formed to be projected in the optical axis direction from the surface of lens 300, and even in this case, there is a problem of damage of flash 301 in the cartridge 200, and there is a problem that positioning accuracy is worsened by flash 301 when flash 301 is formed on the surface (reference surface) on the side used for positioning among both surfaces of lens 300, for example.